Ethylene oxide is typically produced by the oxidation of ethylene with oxygen in the presence of a catalyst. The reaction is exothermic.
A problem with ethylene oxide production relates to the fact that as a production run progresses, the catalyst gradually deactivates. This may be compensated for by allowing the catalyst temperature to increase. This will prolong the production run, but at some point an end of the run (EOR) temperature for the production run will occur. This will occur when the rate of production of ethylene oxide declines to a point at which the run is no longer economical. For the production of ethylene oxide the EOR temperature is typically about 270 to 280° C. The start-of-run (SOR) temperature is usually about 220 to 240° C. Therefore, the deactivation of the catalyst can be compensated by a gradual temperature increase. The change of catalysts will require a shut down of the process. These shut downs are time consuming and costly.
During the lifetime of a catalyst in a state of the art process of making ethylene oxide usually 2 to 4 kilotons of ethylene oxide are produced per cubic meter of catalyst, typically under a work rate of usually 150 to 250 kilograms of produced ethylene oxide per cubic meter per catalyst per hour. The selectivity is depending on the catalyst type, it is usually about 75 to 82% for a high activity catalyst and 82 to 89%for a high selectivity catalyst.
The process of making ethylene oxide is typically conducted in a fixed bed reactor using catalysts in the form of extrudes having dimensions of 3-12 mm as described in US 2008/0081920 and EP 266 015. Usually high selective catalysts are used with a promoting amount of rhenium of about 0.01 to 15 mmol/kg catalyst (see EP 266 015).
Most recently the process of making ethylene oxide using a microchannel reactor is studied (see WO 2008/030467, WO 2006/020709, WO 2007/071739 and US 2008/0031788). Typically, the catalyst is used in the form of a thin coat on the reactor wall. It is well known that wall coated microchannel reactors offer a good heat removal and allow to obtain a stable catalyst operation. However, the catalyst volume ratio to the reactor volume is too low to offer the world scale production capacity of about 150-250 kt/a. Thus, no commercial process is yet available.